The aim of this project is the thermodynamic characterization of the polymerization (gelation) of sickle cell hemoglobin. We have shown how osmotic stress of deoxyhemoglobin S solutions can create the gel state and that the chemical potentials of these preparations can be measured both below and above the gel phase transition. The information so obtained should yield the enthalpy and entropy of gelation, better assays of gelation inhibiting ligands, a measure of molecular contact energies, and data to test theories of deoxyhemoglobin S polymerization and alignment.